Centrifugal pump

ABSTRACT

A centrifugal pump has at least one impeller, a pump housing and an electrical motor. The pump has a Q-H pump curve having a head H 0  at zero flow and a head H ref  corresponding to the highest hydraulic power, and that H ref  is greater than H 0 . The pump has low energy consumption rate, especially at low flow corresponding to the conditions in which the pump is operated most of the time. Thus, the pump according to the invention is less energy consuming than the prior art centrifugal pumps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Section 371 of International Application No. PCT/EP2011/061741, filed Jul. 11, 2011, which was published in the English language on Mar. 1, 2012, under International Publication No. WO 2012/025289 A1 and the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Embodiments of the present invention generally relate to a single speed circulator pump. Embodiments of the invention more particularly relate to a circulator pump having a low energy consumption rate in the typical mode of operation.

It is known to reduce the energy consumption rate of a pump by regulating the speed of the pump. This may, for example, be done by using a frequency converter in a pump. This solution is however relatively technically demanding and expensive. Therefore, it is desirable to have a cheaper alternative to this solution.

When the speed of the pump can be changed during operation it is possible to fit the pump speed to the actual pressure and flow demand, however when a single speed pump is operated, a lot of energy is used to build up a higher pressure than required. Therefore, unregulated pumps normally are energy consuming. Normally a pump is only required to perform to its maximum about 5-10% of the time and hence a lot of energy can be saved by adjusting the pump to actual demand.

It is possible to regulate a pump by using various regulation methods such as proportional pressure and constant pressure regulation. Speed regulation of pumps, however, requires regulation components such as a frequency converter that is an expensive additional feature to the pump.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is desirable to provide a less expensive pump that has a reduced energy consumption rate.

Preferred embodiments, benefits and further scope of applicability of the present invention will become apparent from the claims and the description given hereinafter.

The centrifugal pump according to embodiments of the invention includes at least one impeller, a pump housing and an electrical motor. The pump has a Q-H pump curve with a head H₀ at zero flow and a head H_(ref) corresponding to the highest hydraulic power, where H_(ref) is greater than H₀. Therefore, the pump has low energy consumption rate, especially at low flow corresponding to the conditions in which the pump is operated most of the time. Thus, the pump according to the invention is less energy consuming than the prior art centrifugal pumps.

In one embodiment of the invention the at least one impeller includes impeller blades that are shaped in a manner so that that H_(ref) is greater than H₀. If the impeller blades are forward swept, for example, H_(ref) would be greater than H₀ in the Q-H pump curve (where the head at zero flow is denoted H₀ and where the head corresponding to the highest hydraulic power is denoted H_(ref)).

The forward swept blades are swept or curved from the radial inner side to the radial outer side in rotational direction.

In one embodiment of the invention the first part of the Q-H curve for the pump is an increasing function of the flow. Hereby the pump can be achieved to have a Q-H curve where H_(ref) is greater than H₀ and more specifically a pump having a low energy consumption rate at low flow.

It is also possible to have a pump where the entire Q-H curve is an increasing function of the flow.

In another embodiment of the invention, the last part of the Q-H curve is a decreasing function of the flow. Hereby it can be achieved that a pump has a decreasing power consumption rate that so that overload of the motor can be avoided. There may be several ways of achieving that the last part of the Q-H curve is a decreasing function. This may, for example, be achieved by choosing a pump housing geometry that restricts the flow rate at high head. For example the pump housing may be designed in such way that the cross sectional area of the volute is reduced or can be reduced as a function of the head. This will cause a restricted flow at high head. Further, it may for example be also possible to use the special design of the impeller to achieve a restricted flow at high head. For example the impeller may be configured so that the distance between the front plate and the back plate can be altered as a function of the head.

In one embodiment of the invention the pump housing and/or the impeller is configured to introduce flow restriction such that the end part of the Q-H curve as a function of the flow is decreasing. The term “flow restriction” is means an object or device that restricts the flow. Flow restriction devices may, for example, be an impeller or a pump housing having a specific geometry.

In another embodiment of the invention the impeller has forward swept blades. Forward swept impeller blades may contribute to an increasing Q-H curve. Moreover, the size of the impeller may be minimized because an impeller with forward swept impeller blades is capable of creating a higher flow than an impeller with backward swept impeller blades given the same conditions. The impeller may be constructed in a various ways even though the impeller has forward swept impeller blades.

In another embodiment of the invention the pump has a synchronous motor. This may be an advantage due to the relative high efficiency of synchronous motors especially at low flow.

The synchronous motor operates synchronously with line frequency. The rotational speed is determined by the number of pairs of poles and the line frequency. A synchronous motor is highly efficient and thus by using a synchronous motor it is possible to achieve a pump with a low energy consumption rate.

In one embodiment according to the invention the motor is working with constant speed during operation. This can be achieved by using a synchronous motor.

In one embodiment according to the invention the pump is a circulator pump. The circulator pump may be a glandless (wet-runner) pump. This pump may be used for heating, domestic hot water and air-conditioning applications, for example.

In another embodiment according to the invention the motor is a line start permanent magnet motor. A line star permanent magnet motor is basically a combination of an asynchronous motor and a synchronous motor with fixed magnetization. In a line start permanent magnet motor there is no field winding, instead permanent magnets are used in order to provide the necessary excitation flux.

A synchronous motor without a rotor winding has no net torque at the speeds different from the synchronous. In order to start the motor from a constant frequency supply (such as the mains) some kind of start winding in the rotor has to be used. During the start, currents are induced in the rotor winding. These currents interact with the stator flux field to produce an asynchronous torque that accelerates the rotor. When the rotor speed is sufficiently close to synchronous speed, and on condition that load torque and inertia are not too high, the rotor will be pulled into synchronism. After the rotor has been synchronised the asynchronous torque vanishes and the motor acts as a synchronous motor except that the rotor magnetization is supplied by permanent magnets and not by a DC-current in a field winding.

In one embodiment according to the invention the impeller blades are arced and distributed symmetrically along the periphery of the impeller plate. By this impeller construction it is possible to generate a great flow and achieve the desired Q-H pump curve where

the first part of the Q-H curve is an increasing function of the flow;

that last part of the Q-H curve is a decreasing function of the flow and

H_(ref) is greater than H₀ (where H_(ref) is the head corresponding to the highest hydraulic power and H₀ is the head at zero flow).

In another embodiment according to the invention the impeller includes a first set of impeller blades and a second set of blades, wherein the first set of impeller blades are longer than the second set of impeller blades and where the first set of impeller blades and the second set of impeller blades are distributed alternately along the periphery of the impeller plate. Hereby a Q-H curve having the desired properties can be achieved.

In one embodiment according to the invention (⅔)·H_(ref)≧H₀. A pump having a Q-H curve with these properties will be significantly less energy consuming than the prior art centrifugal pumps.

It would also be possible to have a pump according to the invention where (3/5)H_(ref)≧H₀. A pump with such a Q-H curve would also be significantly less energy consuming than the prior art centrifugal pumps.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 shows a Q-H curve of one embodiment according to the invention;

FIG. 2 is a prior art Q-H curve;

FIG. 3 a illustrates the prior art Q-H curve shown in FIG. 2;

FIG. 3 b shows the power-flow curve for a pump having the Q-H curve illustrated in FIG. 3 a;

FIG. 4 a illustrates the Q-H curve shown in FIG. 1;

FIG. 4 b shows the power-flow curve for a pump having the Q-H curve illustrated in FIG. 4 a;

FIG. 5 is a comparison of the power-flow curves illustrated in FIG. 3 a and FIG. 4 a

FIG. 6 a shows the Q-H curve according to another embodiment of the invention;

FIG. 6 b shows the Q-H curve according to a third embodiment of the invention;

FIG. 7 a illustrates a schematically view of Q-H curves for different impeller blade angles;

FIG. 7 b illustrates a schematically view of three different impeller types;

FIG. 8 illustrates an impeller according to one embodiment of the invention;

FIG. 9 illustrates an impeller according to one embodiment of the invention; and

FIG. 10 illustrates an impeller according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention defined by the claims will become apparent to those skilled in the art from this detailed description.

The pumping performance of a centrifugal pump is frequently expressed in the form of a Q-H curve, depicting the head H (normally measured in m) as a function of the flow Q (for instance measured in m³/h) of the pump. The slope of the Q-H curve is determined by the pump construction and particularly by the design of the impeller.

The majority of circulator pumps are provided with impellers having backwards swept impeller blades. These types of impellers generate a Q-H curve where the head is decreasing with increasing flow (see FIG. 2).

The hydraulic power P_(h) is given by the following equation (1)

P _(h) =H·g·ρ·Q   (1)

where H is the head, g is gravity, ρ is the density of the fluid and Q is the flow.

In order to calculate the hydraulic efficiency η_(h) of the hydraulic part of the pump (the pump housing and the impeller) one needs to know the power P_(n) supplied to the hydraulic part of the pump as well as the power P_(h) that the pump transfers to the fluid. This is given by the following equation (2)

$\begin{matrix} {\eta_{h} = \frac{P_{h}}{P_{n}}} & (2) \end{matrix}$

In order to calculate the total efficiency η_(t) of the pump one has to know the total power P_(t) supplied to the control (if any) and the motor as well as the power P_(h) that the pump transfers to the fluid. This is given by the following equation (3)

$\begin{matrix} {\eta_{t} = \frac{P_{h}}{P_{t}}} & (3) \end{matrix}$

The total efficiency η_(t) of the pump is given by the following equation (4)

η_(t)=η_(control)·η_(motor)·η_(h)   (4)

where η_(control) is the efficiency of the control and η_(motor) motor is the efficiency of the motor.

The flow where the pump has the highest efficiency is referred to as the best point.

When working with the Q-H curve, one often focuses on the head H₀ at zero flow and the head H_(ref) corresponding to the highest hydraulic power P_(h, max). These points are characteristics of the pump. In the Q-H curves of the prior art centrifugal pumps H₀ is greater than H_(ref) and the H curve is normally a decreasing function of Q. If we look at the power-flow curve for the prior art centrifugal pumps, the power consumption is relatively high, especially at low flow. The pumps are operated in the low flow area the majority of the time. Therefore, it would be advantageous to have a pump that is less energy consuming, especially in the low flow area.

Speed regulated pumps are used to adjust the generated pressure according to the actual demand. Speed regulation requires a regulation of the motor. In many pumps a frequency converter is used to regulate the speed of the motor, however; such solution is expensive and technically demanding. On the other hand, many unregulated motors have a low efficiency. A high efficiency, especially at low loads, can be achieved by using a line start permanent magnet motor. A line start permanent magnet motor has typically a significant position dependent difference in the inductance (difference in the D- and Q-axis inductance). This difference gives a reluctance torque, so that the total torque production from the motor is given by the combination of the alignment torque and the reluctance torque. By tailoring the geometry to the hydraulic load and the specific application the reluctance torque can be used to increase the efficiency of the motor at lower load (at a slightly reduced efficiency at maximum load). Hereby the energy consumption can be lowered.

Combining a line start motor and a pump having a Q-H pump curve where H_(ref) is greater than H₀ may eliminate the use of a frequency converter. A pump with a high efficiency may be achieved by combining a line start motor and a pump having a Q-H pump curve where H_(ref) is greater than H₀. Therefore, the present invention may make it possible to make a high efficiency that is cheaper than the prior art high efficiency pump.

Traditionally, unregulated pumps are equipped with manual speed change-over devices e.g., a rotary knob that may be set in three different speeds. Most pump manufacturers have focused on producing pumps having different regulation curves. Line start motors are generally used for applications in which an exact and constant speed is required. One example of such application is a conveyor belt.

If a pump is provided with a line start motor there is no speed regulation option. Therefore, pump manufactures use other types of motors for their pumps. In embodiments of the present invention, however, the pump is equipped with a line start motor. Hereby it is achieved that the efficiency is increased compared with traditional asynchronous motors, especially at the lower loads. Therefore, the line start motor makes it possible to save energy.

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a Q-H curve 4 according to a preferred embodiment of the present invention is illustrated in FIG. 1. The Q-H curve 4 illustrates the hydraulic head (H) 2 (hereinafter referred to as “head”) as a function of the flow (Q) 6. It can be seen from FIG. 1 that the first part 8 (approximately the first two thirds) of the Q-H curve 4 has a positive slope. This means that the first part 8 of the Q-H curve 4 is increasing. Moreover, it can bee seen that the last part 10 (approximately the last third) of the Q-H curve 4 has a negative slope. Accordingly, the last part 10 of the Q-H curve 4 is decreasing. It can be seen that H_(ref) 30 is greater than H₀ 28 (where H_(ref) is the head corresponding to the highest hydraulic power and H₀ is the head at zero flow). Moreover, the global maximum 24 of the Q-H curve 4 is indicated and it can be seen that (QH)_(ref) is offset slightly to the right side of the global maximum 24 of the Q-H curve 4.

FIG. 2 shows a prior art Q-H curve 4 (the head 2 as function of the flow 6). It can be seen that the head (H) 2 is a decreasing function of the flow (Q) 6. This Q-H curve 4 corresponds to the Q-H curve of a typical centrifugal type circulator pump. It can be seen that H₀ 28 is greater than H_(ref) 30 (where H_(ref) is the head corresponding to the highest hydraulic power and H₀ is the head at zero flow).

FIG. 3 a illustrates the Q-H curve 4 shown in FIG. 2 and FIG. 3 b illustrates the corresponding power-flow curve 12 (the power (P) 14 as function of the flow (Q) 6) for a prior art pump having the Q-H curve 4 illustrated in FIG. 3 a. In FIG. 3 b it can be seen that the maximal flow Q₁₀₀% 22, the flow Q₂₅% 16 corresponding to 25% of the maximal flow Q₁₀₀% 22, the flow Q₅₀% 18 corresponding to 50% of the maximal flow Q₁₀₀% 22 and the flow Q75% 20 corresponding to 75% of the maximal flow Q₁₀₀% 22 are lying relatively high (the indicated power values 16, 18, 20 and 22) on the power-flow curve 12.

FIG. 4 a illustrates the Q-H curve 4 shown in FIG. 1 and FIG. 4 b illustrates the power-flow curve 12 (the power (P) 14 as function of the flow (Q) 6) for a pump having the Q-H curve 4 illustrated in FIG. 4 a. In FIG. 4 b it can be seen that the flow Q25% 16 corresponding to 25% of the maximal flow Q₁₀₀% 22, the flow Q₅₀% 18 corresponding to 50% of the maximal flow Q₁₀₀% 22 and the flow Q₇₅% 20 corresponding to 75% of the maximal flow Q₁₀₀% 22 are associated with lower power values 16, 18, 20 than in the prior art pump curve 4 illustrated in FIG. 3 b.

FIG. 5 shows a comparison of the power-flow curves illustrated in FIG. 3 a and FIG. 4 a. It can be seen from FIG. 5 that the maximal flow Q₁₀₀% 22′, 22″ of both the prior art power-flow curve 38 and for the power-flow curve 40 corresponding to a pump having the Q-H curve 4 according to the invention (illustrated in FIG. 4 a) are almost coinciding. If we look at the power-flow curve 40 corresponding to the invention is can be seen that the power value at the flow Q₂₅% 16″ corresponding to 25% of the maximal flow Q₁₀₀% is significantly lower than the prior art power value at the flow Q₂₅% 16′. It can also be seen that the power value at the flow Q₅₀% 18″ corresponding to 50% of the maximal flow Q₁₀₀% is significantly lower than the prior art power value at the flow Q₅₀% 18′. Besides, the power value at the flow Q₇₅% 20″ corresponding to 75% of the maximal flow Q₁₀₀% is significantly lower than the prior art power value at the flow Q₇₅% 20′. Accordingly, the pump according to the present invention will have a low energy consumption rate.

FIG. 6 a illustrates the Q-H curve 4 according to an embodiment of the invention. In the Q-H curve 4 the head (H) 2 is plotted against the flow (Q) 6. Approximately the first two thirds 8 of the Q-H curve 4 has a positive slope and thus the first part 8 of the Q-H curve 4 is increasing. Approximately the last third 10 of the Q-H curve 4 has a negative slope and therefore, the last part 10 of the Q-H curve 4 is decreasing. H_(ref) 30 is greater than H₀ 28 (where H_(ref) is the head corresponding to the highest hydraulic power and H₀ is the head at zero flow). Besides, the global maximum 24 of the Q-H curve 4 is and (QH)_(ref) 26 are almost coinciding.

FIG. 6 b illustrates a Q-H curve 4 according to another embodiment of the invention. This Q-H curve 4 is almost similar to the Q-H curve 4 shown in FIG. 6 a, however; the global maximum 24 of the Q-H curve 4 is and (QH)_(ref) 26 are displaced relative to one another. (QH)_(ref) 26 is located to the right for the global maximum 24 of the Q-H curve 4.

FIG. 7 a illustrates a schematic view of theoretical Q-H curves 42, 44, 46 for different impeller blade angels. In these curves 42, 44, 46 the height 2 is plotted against the flow 6. The blade angle β is indicated in FIG. 7 b and represents the angle between the outer periphery of the impeller and the outer side of the impeller blade. FIG. 7 a shows that backward swept impellers have a decreasing theoretical Q-H curve 46. FIG. 7 a also shows that forward swept impellers have an increasing theoretical Q-H curve 46. It can also be seen that the theoretical Q-H curve 44 of a neutral impeller construction where the blade angle β between the outer periphery of the impeller and the outer side of the impeller blade is 90 degrees is flat (horizontal).

The term “forward swept blades” means that the angle β is greater than 90°, where β is defined as the angle between the outer periphery of the impeller 32 and the outer side of the impeller blade 34. The term “backwards swept blades” means that the angle β is less than 90°. The term “neutral swept blades” 34 means that the angle β is equal to 90°.

FIG. 7 b illustrates a schematic view of three different impeller 32 types where the blade angle β is under 90 degrees, equal to 90 degrees and more than 90 degrees respectively. The blades 34 as well as the rotational direction of the impeller 36 are indicated in the figure.

FIG. 8 shows an impeller 32 according to one embodiment of the invention. The impeller 32 includes a first set of impeller blades 34 and a second set of blades 35, where the first set of impeller blades 34 are longer than the second set of impeller blades 35 and where the first set of impeller blades 34 and the second set of impeller blades 35 are distributed alternately along the periphery of the impeller plate 48. The first set of impeller blades 34 includes ten blades and the second set of impeller blades 35 also includes ten blades. When one examines the rotational direction 36 of the impeller 32, it can be seen that both the first set of impeller blades 34 and the second set of blades 35 are forward swept because the angle between the outer periphery of the impeller 32 and the outer side of the impeller blades 34, 35 is greater than 90°.

FIG. 9 illustrates a typical impeller 32 having a number of backwards swept impeller blades 34, i.e., the impeller blades are swept or curved against the rotational direction 36. It is indicated that the rotational direction 36 is counter clockwise—the rotational speed is denoted ω and the radius r of the impeller 32 is also indicated. The absolute velocity C of the fluid is given by the sum of the tangential velocity U of the impeller 32 and the relative velocity W relative to the impeller 32. Theses velocities C, U and W are indicated with arrows. The magnitude of the tangential velocity U of the impeller 32 is given by the product of the radius r and the rotational speed ω:

|U|=r·ω  (5)

The blade angle β is less than 90 degrees.

FIG. 10 illustrates an impeller 32 with a forward swept impeller blade 34, i.e., the blades are swept in rotational direction 36. It is indicated that the rotational direction 36 is counter clockwise like in FIG. 9. The projection C_(U) of C in the tangential plane is indicated and it can be seen that this forward swept impeller has the following characteristic:

C_(U)>U   (6)

It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims. 

1.-12. (canceled)
 13. A centrifugal type circulator pump comprising at least one impeller (32), a pump housing and an electrical motor, where the pump has a Q-H pump curve (4) having a head n₀ (28) at zero flow and a head, H_(ref) (30), corresponding to the highest hydraulic power, wherein H_(ref) (30) is greater than H₀ (28).
 14. The centrifugal pump according to claim 13, wherein the at least one impeller (32) comprises impeller blades (34) that are shaped in a manner so that that H_(ref) (30) is greater than H₀ (28).
 15. The centrifugal pump according to claim 13, wherein a first part (8) of the Q-H curve (4) is an increasing function of a flow (6).
 16. The centrifugal pump according to claim 13 wherein a last part (10) of the Q-H curve (4) is a decreasing function of a flow (6).
 17. The centrifugal pump according to claim 13 wherein the pump housing and/or the impeller (32) is configured to introduce a flow restriction that causes an end part (10) of the Q-H curve (4 ) to be a decreasing function of a flow (6).
 18. The centrifugal pump according to claim 13, wherein the impeller (32) has forward swept blades (34).
 19. The centrifugal pump according to claim 13, wherein the motor is a synchronous motor.
 20. The centrifugal pump according to claim 13, wherein the centrifugal pump is a wet-runner type pump.
 21. The centrifugal pump according to claim 13, wherein the motor is a line start permanent magnet motor.
 22. The centrifugal pump according to claim 14, wherein the impeller blades (34) are arced and distributed symmetrically along a periphery of an impeller plate (48).
 23. The centrifugal pump according to claim 13, wherein the impeller (32) comprises a first set of impeller blades (34) and a second set of impeller blades (35), where the first set of impeller blades (34) are longer than the second set of impeller blades (35) and where the first set of impeller blades (34) and the second set of impeller blades (35) are distributed alternately along a periphery of an impeller plate (48).
 24. The centrifugal pump according to claim 13 wherein (⅔)·H_(ref)≧H₀.
 25. The centrifugal pump according to claim 13, wherein (⅗) H_(ref)≧H₀. 